The present invention is directed to an improved actuator for plug-type values. While the particular use made of the valve does not constitute a limitation of the present invention, it is particulary well suited for use with large valves or high pressure valves.
Prior art workers have utilized a number of arrangements of cam slots and cam follower means for translating linear motion into rotative motion, or vice versa, in association with the actuation of valves. U.S. Pat. Nos. 2,596,075 and 3,492,880 are exemplary of those prior art actuators for valves of the plug type wherein, when the plug is to be shifted from its valve-closed position to its valve-open position, it is first lifted vertically and thereafter rotated. When the valve plug is to be shifted from its valve-open position to its valve-closed position, it is first rotated and thereafter lowered to its valve-closed position. In the structure of both of these patents, the vertical linear motion and the rotative motion are wholly separate, occurring one after another.
The above mentioned copending application teaches an improved plug valve actuator wherein, when the actuator shifts the plug from its valve-closed position to its valve-open position, it first lifts the plug vertically without rotation and thereafter simultaneously lifts and rotates the valve to its final valve-open position. During the valve-closing procedure, the actuator first simultaneously rotates and lowers the plug, and thereafter continues to lower the plug without rotation into its final valve-closed and sealed position. As a result, the resilient seals of the plug are never rotated when in contact with the valve body, thus assuring prevention of abrasion of the resilient seals. Furthermore, rotation of the plug 90.degree. between its valve-open and valve-closed positions is accomplished in a minimum of vertical travel of the plug and since this rotation is accomplished simultaneously with a portion of the vertical shifting of the plug during both the opening and closing operations, the valve body and plug can be compact.
The teachings of the above-noted copending application are incorporated herein by reference. Briefly, the copending application teaches the provision of an actuator for a plug valve of the type having a body with a central chamber and diametrically opposed inlet and outlet ports communicating with the central chamber. The valve has a plug within the chamber, the plug having a transverse passage therethrough and an upstanding stem.
The plug has a first, upper valve-open position within the chamber with the transverse plug passage being in alignment with the inlet and outlet ports. The plug has a second, lower, valve-closed position within the chamber wherein its transverse passage is oriented at 90.degree. to the inlet and outlet ports and wherein seal means on the plug are in sealing engagement with the chamber wall about the inlet and outlet ports. The top of the chamber is closed by a bonnet having a packing gland through which the plug stem extends upwardly.
The actuator comprises a hollow, cylindrical yoke, the lower end of which is affixed to the bonnet with the plug stem extending partway into the yoke. A bearing cap is mounted at the upper end of the yoke. A drive nut, having a threaded axial bore and a hand wheel or other manual manipulator affixed thereto, is rotatively mounted in the bearing cap. A threaded stem is engaged in the drive nut. The lower end of the threaded stem and the upper end of the plug stem are both non-rotatively affixed to a cylindrical coupling within the yoke.
In one embodiment of the invention, the cylindrical coupling has a pair of diametrically opposed, identical, L-shaped cam slots. Each of the L-shaped cam slots has a first vertical portion and a second portion which extends 90.degree. about the coupling and slopes downwardly throughout its length. The yoke has two cam pins threadedly engaged in diametrically opposed perforations in the yoke, the innermost ends of the cam pins being unthreaded and engaged in the cam slots of the coupling. In a second embodiment of the invention of the copending application, a pair of identical, diametrically opposed cam slots are formed in the body of the yoke itself. These cam slots are similar to those just described but are of the inverted L-shaped configuration. Thus, the cam slots formed in the yoke each have a first portion which extends 90.degree. about the yoke and slopes downwardly from their beginning points to the juncture with their second portions which extend vertically downwardly. In this second embodiment, the coupling within the yoke carries a pair of cam followers, each engaged in one of the yoke cam slots.
In both embodiments of the invention, the configuration of the cam slots is such that upon turning the drive nut in one direction, the plug (in its valve-open position) will be simultaneously partially lowered and turned 90.degree.. Thereafter, continued turning of the drive nut will lower the plug without rotation to its valve-closed and sealed position. When the drive nut is turned in the opposite direction, the plug (in its valve-closed position) will first be lifted vertically without rotation out of sealing relationship with chamber inlet and outlet ports. Continued rotation of the value nut in this direction will cause the plug to be simultaneously lifted and rotated 90.degree. to its full valve-open position.
In basic valve design of this kind, it is desirable to keep the height of the body and the plug to a minimum, for rigidity and to minimize the cost of material and machining. Since the vertical travel during rotation of the plug 90.degree. between its valve-open and valve-closed positions is a function of the angle of the cam slots in the cylindrical coupling, the selection of the cam slot angle is a trade-off between low angle, short body and minimum torque output on the one hand and high angle, long body and high torque output on the other. The present invention teaches a drive cam means introduced between the coupling and the valve stem in order to increase torque output of the inclined cam slots without changing or increasing the height of the valve body and plug. The valve actuator of the present invention still comprises a minimum of parts, all of which are readily servicable and replaceable. The actuator is extremely simple and compact in construction and inexpensive to manufacture. It remains self-locking against torque imparted to the plug by the fluid medium passing through the valve.